The present invention relates to a method and device for controlling the cornering speed of a vehicle.
If a vehicle is traveling on surfaces having low coefficients of friction, instabilities such as fishtailing at the rear axle can occur during steering maneuvers such as driving on a curve or during evasive maneuvers, because the transverse forces on the wheels are too small to ensure stable cornering behavior. This oversteering behavior must be compensated for by suitable corrective control actions.
German Patent Application 19907633 teaches a method and a device for stabilization of a vehicle, especially for prevention of rollover of a vehicle around a vehicle axis oriented in a longitudinal direction of the vehicle, especially during cornering. For this purpose, a variable describing the transverse dynamics of the vehicle is determined. This variable is compared with at least one characteristic value, especially with a threshold value for this variable. If the variable describing the transverse dynamics of the vehicle is larger than the characteristic value or equal to the characteristic value, the speed of the vehicle is reduced to a predefinable limit value of cornering speed or is maintained at a predefinable limit value of cornering speed by braking actions on at least one wheel and/or by engine actions, by which the engine""s torque output is reduced, and/or by retarder actions. A variable describing the lateral acceleration is used as the variable describing the transverse dynamics of a vehicle; this variable being determined as a function of the vehicle""s speed and steering angle.
For an exact determination of the limit value of cornering speed, it is necessary to know the coefficient of friction. If inhomogeneous coefficients of friction are present, it would be necessary to determine the coefficient of friction for each wheel. Furthermore, the limit value of cornering speed at which the wheel completely or partly loses its lateral traction also depends on acceleration and braking slip. Since these parameters are not taken into consideration in the known method and known device, the method and the device are suitable to only a limited extent in practice.
Accordingly, it is desired to provide a method and device or apparatus for controlling the cornering speed of a vehicle, while overcoming the disadvantages associated with prior art methods and devices.
Generally speaking, in accordance with the present invention, an improved method and device or apparatus are provided for controlling the cornering speed of a vehicle, whereby the vehicle can drive stably with maximum traction on a curve.
In one aspect of the present invention, a method for controlling the cornering speed of a vehicle is provided including the steps of determining a body slip angle of the vehicle and comparing the body slip angle with a body slip-angle threshold value, and in response to a deviation of the body slip angle from the body slip-angle threshold value taking a corrective action with respect to the engine to control the cornering speed of the vehicle.
In another aspect of the present invention, the body slip angle of the vehicle is calculated using the vehicle""s lateral acceleration, yaw angular velocity and actual speed.
In yet another aspect of the present invention a device or apparatus is provided for controlling the cornering speed of a vehicle having sensors for determining the speed, the lateral acceleration and the yaw angular velocity of the vehicle, a computing device for computing a body slip angle from the lateral acceleration, the yaw angular velocity and the actual speed of the vehicle, a threshold circuit for comparison of the body slip angle with a body slip-angle threshold value, a weighting circuit which is connected to the output side of the threshold circuit, and which determines a correction value proportional to the determined body slip angle, a first summation point, in which a set speed of the vehicle is reduced from the actual speed of the vehicle by the correction value, a second summation point in which the actual speed of the vehicle is compared with the set speed of the vehicle in order to calculate a value of the control deviation, and a PD controller for adjusting the engine torque as a function of the value of the control deviation.
Accordingly, an object of the present invention is to provide a simple, effective and practical method and apparatus for controlling the cornering speed of a vehicle, whereby the vehicle can drive stably with maximum traction on a curve.
It is a further object of the present invention to provide a device or an apparatus for performing the method.
It is another object of the present invention to provide a method and an apparatus for controlling the cornering speed of a vehicle by controlling the vehicle""s engine as a function of the body slip angle.
Still other objects and advantages of the present invention will in part be obvious and will in part be apparent from the specification.
The present invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and embodies features of construction, combination of elements, and arrangement of parts which are adapted to effect such steps, all as exemplified in the detailed disclosure hereinafter set forth, and the scope of the invention will be indicated in the claims.